Method of producing selenium charge electrophotographic recording plates

ABSTRACT

This relates to a method of producing an electrophotographic recording plate having a non-conducting selenium layer. A small portion of semiconducting material, especially chemical compounds of cadmium, zinc or titanium, is sputtered onto the selenium surface in a glow discharge.

United States Patent 11 1 1111 3,901,783

Raiim et a]. 1 Aug. 26, 1975 [54] METHOD OF PRODUCING SELENIUM 2,903,6319/1959 Perotte 204/192 CHARGE ELECTROPHOTOGRAPHIC 3,650,737 3/1972Maissel Ct a1. 204/192 RECORDING PLATES 3,733.258 5/1973 Hanak et a1.204/192 [75] Inventors: Helmut Raiim, Nurnberg; John E. OTHERPUBUCATlONS Segain, Gunzcnhausen, both of Tanaka, Photoconductivity ofCase Films Prepared Germany by a Vapor Evaporating-Reactive Sputtering[73] Assignee: International Standard Electric Method," Japanese Journalof pp Physics,

corporationq New York 9, No. 9 (September 1970), pages 10701077.

[22] Filed: 1974 Primary Examiner-Oscar R. Vertiz [21 App]. No.: 439,807Assistant Examiner-Wayne A. Lange] Attorney, Agent, or FirmJohn T.OHalloran;

[30] Foreign Application Priority Data Menottl J. L0mbard1, Jr.; Vmcentlngrass1a Feb. 9, 1973 Germany 2306332 Feb. 9, 1973 Germany 2306333 [57]ABSTRACT Th ltt' thdf d' lt h- 1521 11.5. C1. 204/192 g g g g gg g 31;3335;35 :153; [51] Int. Cl. C23c 15/00 lenium layer. A small portion ofsemiconducting mate- [58] Fleld of Search 204/192 rial especiallychemical compounds of cadmium, Zinc or titanium, is sputtered onto theselenium surface in a [56] References Cited glow discharge UNITED STATESPATENTS 2,189,580 2/1940 Hewlett 204 192 9 Clam, N0 Drawmgs METHOD OFPRODUCING SELENIUM CHARGE ELECTROPHOTOGRAPHIC RECORDING PLATESBACKGROUND OF THE INVENTION The present invention relates to a processfor preparing a selenium charge electrophotographic recording plate witha non-conducting selenium layer arranged on a metal substrate.

In the electrophotographic process there are used recording plates witha conducting substrate on which there is deposited a photoconductivelayer of semiconducting material on which a charge pattern is producedby the charge and exposure to light, corresponding to the image pattern.This charge pattern is made visible by the application of a suitableinking powder which, in the course of a further step of the process, istransferred from the recording plate to a sheet of paper where it isfixed. In practice, it has proved particularly suitable to use recordingplates employing selenium as the semiconducting material. Certainadditives to the selenium improve the electrophotographic properties.The metal substrate on which the selenium layer is deposited, consistseither of a rigid metal plate or of a metal cylinder, or else of aflexible metal foil, such as a steel tape. Onto this metal substrate theselenium is usually deposited by way of evaporation under vacuum.

The known electrophotographic recording plates with a selenium layerstill have certain disadvantages. First, it is impossible for largerblack areas to be reproduced as such, because the charge on the seleniumlayer is chiefly positioned in the marginal areas of the thus imagedsurfaces.

Second, only pure black-and-white patterns can be reducedsatisfactorily, whereas patterns with medium shades yield poorreproduction. There has been an attempt to overcome this disadvantage byusing optical rasters during the imaging and disintegrating the imageinto a great number of individual image spots (points). However, thisdisintegration is unwanted in many cases, especially in the reproductionof photographs. Further, this does not substantially increase the grayscales to be reproduced.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide a process of preparing electrophotographic recording plates witha non-conducting selenium layer which permits reproduction of largerblack areas, and with the aid of which it is possible to reproduce agreater number of different gray scales.

According to a broad aspect of the invention, there is provided a methodof preparing a selenium charge electrophotographic recording platehaving a selenium layer deposited on a metal substrate comprising thesteps of depositing selenium on a metal substrate by evaporation undervacuum to form a selenium layer, depositing a thin coating of asemiconducting material on a metal plate, subjecting the selenium coatedmetal substrate and said metal plate having a semiconducting materialthereon to a glow discharge whereby a portion of said semiconductingmaterial is deposited on said selenium layer.

Although the deposited amounts of semiconducting substance are extremelysmall, there is achieved a substantial improvement in the recordingplates, permitting the reproduction of larger black areas as well as agreat number of gray scales with the aid of such recording plates.

The aforementioned advantages will only be achieved when the applicationis effected in the course of a glow discharge. The glow discharge itselfalso has an influence upon the improvement in the electrophotographicreproducibility of the selenium layer.

The above and other objects of the present invention will be moreclearly understood from the following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENT The application of thesemiconducting substance is effected in such a way that a metal plateprovided with a coating of the semiconducting substance to be used, isarranged as the cathode in a glow discharge, while the anode is formedby the selenium layer of the recording plate. Both the cathode and theanode are arranged at a certain distance apart each other in a suitablegas atmosphere. As gases for the glow discharge, it has provedparticularly suitable to use inert gases, such as nitrogen or raregases.

A further improvement in the reproducibility of the selenium layers canbe obtained in that the metal plate used as the cathode, is provided onits surface facing the selenium surface, with a pattern of recesses.These recesses may also extend entirely through the metal plate formingthe cathode, so that the cathode is a perforated metal plate.

The glow discharge is preferably carried out under a pressure in theorder of 10 to 10 torr (mm Hg). In the course of this, there is used avoltage in the order of 800 to 2,000 V, with the current flow amountingto values between 20 and 200 milliamperes. The selenium surface isexposed to this glow discharge for a period of time ranging between halfa minute and sixty minutes. Preferably, an inert gas is used for theglow discharge, hence a gas which, under the glow-discharge conditionsdoes not chemically combine with either the substrate material or theselenium. As a suitable inert gas, it is possible to use e.g. nitrogenor else a rare gas, such as argon.

Surprisingly, oxygen may be used as the gas for the glow discharge.Oxygen, of course, reacts with the selenium, but this reaction has noinfluence upon the desired effect. No disadvantageous effects upon theelectrophotographic properties of the selenium have been noticed whenusing oxygen.

Suitable semiconducting materials for depositing onto the seleniumsurface are, in particular, semiconducting cadmium compounds,semiconducting zinc compounds and semiconducting titanium oxide.

Of the semiconducting cadmium compounds, cadmium sulfide and cadmiumselenide are particularly suitable.

Of the semiconducting zinc compounds, zinc oxide and zinc sulfide areparticularly suitable.

In the case of rigid plates, it has proved particularly suitable to usepolished aluminum as the metallic substrate while in the case offlexible foils, polished steel tapes are preferably used.

Onto the completely smooth and well-cleaned metal substrate, theselenium is deposited by way of evaporation under vacuum in the form ofa layer in the order of 10 to microns thick. For improving itselectrophotographic properties, the selenium may still be provided withsmall additions. Thus, for example, it is of advantage to use anaddition of 0.5 per cent by weight of arsenic in order to prevent alater crystallization of the selenium layer. In cases where therecording plates are intended to be exposed to X-rays, it has provedparticularly suitable to provide additions of metals with a high atomicweight, or compounds of such metals. Lead or lead compounds areespecially suitable for this purpose.

The selenium-coated substrate is placed at a suitable distance from ametal plate provided with a thin coating of the semiconducting materialto be deposited, in an inert gas atmosphere under a pressure of l totorr, and a voltage is applied ranging between 800 and 2000 V. The metalplate provided with the layer of semiconducting substance to bedeposited forms the cathode while the selenium layer forms the anode.During glow discharge, there will flow a current ranging between and 200milliamperes. Action lasts for a period ranging between half a minuteand sixty minutes.

The resulting electrophotographic recording plates show substantiallyimproved reproducibility, especially of larger black areas, and permitreproduction of a large number of gray scales.

It is to be understood that the foregoing description of specificexamples of this invention is made by way of example only and is not tobe considered as a limitation on its scope.

As a further means of obtaining the desired increase in the number ofgray scales reproducible, the surface of a selenium layer is subjectedas the cathode to the glow discharge. A polished plate of aluminum ispreferably used as the anode. Glow discharge is carried out under theabove described conditions causing a great number of slightimperfections in the selenium surface during glow discharge. Theimperfections are uniformly distributed over the entire seleniumsurface, however, the disintegration of the image into individual spotsdoes not occur as is the case when using an optical raster.

We claim:

1. A method of preparing a selenium charge electrophotographic recordingplate having a selenium layer deposited on a metal substrate comprisingthe steps of:

depositing selenium on a metal substrate by evaporation under vacuum toform a selenium layer; depositing a thin coating of a semiconductingmaterial selected from the group consisting of cadmium sulfide, zincoxide and zinc sulfide on a metal plate; thereafter sputtering a portionof said semiconducting material on said selenium layer by subjecting theselenium coated metal substrate and said metal plate to a glowdischarge.

2. A method of preparing a selenium charge electrophotographic recordingplate according to claim 1, wherein said glow discharge is carried outunder a pressure within the range of 10 to 10 torr at a voltage withinthe range of 800 to 2,000 volts.

3. A method of preparing a selenium charge electrophotographic recordingplate according to claim 2, wherein said glow discharge is carried outfor a period of time ranging between 30 seconds to minutes.

4. A method of preparing a selenium charge electrophotographic recordingplate according to claim 1, wherein said metal plate has a pattern ofrecesses thereon.

5. A method of preparing a selenium charge electrophotographic recordingplate according to claim 1, wherein said metal plate used as the cathodeis a perforated metal plate.

6. A method of preparing a selenium charge electrophotographic recordingplate according to claim 1, wherein said glow discharge is carried outin an inert gas atmosphere.

7. A method of preparing a selenium charge electrophotographic recordingplate according to claim 1, wherein said glow discharge is carried outin nitrogen.

8. A method of preparing a selenium charge electrophotographic recordingplate according to claim 1, wherein said glow discharge is carried outin OXygen.

9. A method of preparing a selenium charge electrophotographic recordingplate according to claim 1, wherein said metal plate is a polished plateof alumi-

1. A METHOD OF PREPARING A SELENIUM CHARGE ELECTROPHOTOGRAPHIC RECORDINGPLATE HAVING A SELENIUM LAYER DEPOSITED ON A METAL SUBSTRATE COMPRISINGTHE STEPS OF: DEPOSITING SELENIUM ON A METAL SUBSTRATE BY EVAPORATIONUNDER VACUUM TO FORM SELENIUM LAYER, DEPOSITING A THIN COATING OF ASEMICONDUCTING MATERIAL SELECTED FROM THE GROUP CONSISTING OF CADMIUMSULFIDE, ZINC OXIDE AND ZINC SULFIDE ON A METAL PLATE, THEREAFTERSPUTTERING A PORTION OF SAID SEMICONDUCTING MATERIAL ON SAID SELENIUMLAYER BY SUBJECTING THE SELENIUM COATED METAL SUBSTRATE AND SAID METALPLATE TO A GLOW DISCHARGE.
 2. A method of preparing a selenium chargeelectrophotographic recording plate according to claim 1, wherein saidglow discharge is carried out under a pressure within the range of 10 1to 10 2 torr at a voltage within the range of 800 to 2,000 volts.
 3. Amethod of preparing a selenium charge electrophotographic recordingplate according to claim 2, wherein said glow discharge is carried outfor a period of time ranging between 30 seconds to 60 minutes.
 4. Amethod of preparing a selenium charge electrophotographic recordingplate according to claim 1, wherein said metal plate has a pattern ofrecesses thereon.
 5. A method of preparing a selenium chargeelectrophotographic recording plate according to claim 1, wherein saidmetal plate used as the cathode is a perforated metal plate.
 6. A methodof preparing a selenium charge electrophotographic recording plateaccording to claim 1, wherein said glow discharge is carried out in aninert gas atmosphere.
 7. A method of preparing a selenium chargeelectrophotographic recording plate according to claim 1, wherein saidglow discharge is carried out in nitrogen.
 8. A method of preparing aselenium charge electrophotographic recording plate according to claim1, wherein said glow discharge is carried out in oxygen.
 9. A method ofpreparing a selenium charge electrophotographic recording plateaccording to claim 1, wherein said metal plate is a polished plate ofaluminum.